1. Field of the Invention
The present invention relates to a projection exposure apparatus used, for example, in fabricating semiconductor devices or liquid crystal display devices, etc. by a photolithography process, and a method for producing circuit patterns using such a projection exposure apparatus. More particularly, the invention is suitably applicable to the projection exposure apparatus provided with a function, for example, to perform measurement of reticle alignment, registration accuracy, or imaging characteristics of a projection optical system therethrough.
2. Related Background Art
The photolithography process for fabricating semiconductor devices or liquid crystal display devices, etc. uses the projection exposure apparatus for performing exposure of images of patterns on a photomask or reticle (hereinafter, "reticle" is used as an example) through the projection optical system onto a wafer (or glass plate, etc.) coated with a photoresist. In order to perform accurate positioning (reticle alignment) of the reticle relative to a wafer stage on which the wafer is mounted, prior to exposure, such projection exposure apparatus employ an alignment system for simultaneously observing an alignment mark formed on the reticle and a reference mark formed on the wafer stage through the projection optical system.
A reference mark FM1 consisting of four linear patterns shown in FIG. 1A is an example of the reference mark on the wafer stage, used for reticle alignment, and a cross alignment mark RM1 shown in FIG. 1B an example of the mark on the reticle, corresponding to it. The reference mark FM1 is used as reference for positions in mutually orthogonal X direction and Y direction. In this case, for example, when the reference mark is observed through the projection optical system from above the reticle by a two-dimensional image pickup device, the alignment mark RM1 and a reference mark image FM1P are observed as overlapping with each other in an observation field on the reticle, as shown in FIG. 2A. Then, for example reading out an image signal along a scanning line on the image pickup device, corresponding to a scanning line SL parallel to the X direction in FIG. 2A, the signal shown in FIG. 2B is obtained and from this signal, an amount of positional deviation in the X direction, of the alignment mark RM1 is obtained relative to the reference mark image FM1P. Similarly, an amount of positional deviation in the Y direction is also obtained. The reticle alignment is performed by driving the amount of each positional deviation of the alignment mark RM1 thus obtained into a predetermined value.
Meanwhile, attempt has been made to improve imaging performance of the projection optical system in exposure of predetermined patterns by setting an optical filter (hereinafter referred to as a "pupil filter") with predetermined characteristics near the pupil plane of the projection optical system.